Automobile tires are formed from rubber compositions containing natural rubber and/or synthetic diene rubbers as raw materials. Such tires are degraded in the presence of ozone and may eventually be cracked. In order to suppress crack formation and growth in the presence of ozone, rubber compositions contain, for example, additives, including antioxidants, such as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) or poly(2,2,4-trimethyl-1,2-)dihydroquinoline (TMDQ), and petroleum wax.
The antioxidants and petroleum wax in vulcanized rubber migrate (bloom) to the surface of rubber such as tires, thereby protecting the rubber from ozone. Unfortunately, excessive blooming of the antioxidants and petroleum wax in a short period of time causes white discoloration. Also, the antioxidants degraded by ozone cause brown discoloration, and similar excessive blooming of them intensifies brown discoloration. In addition, if wax and the like bloomed on the tire surface form irregularities, diffused reflection of light occurs, making the brown discoloration caused by the degraded antioxidants more noticeable. Thus, the shine of the tires is also lost.
Patent Literature 1 discloses the addition of a polyoxyethylene ether nonionic surfactant for preventing deterioration of tire appearance. Yet, this technique needs improvement in terms of improving discoloration resistance and tire appearance while maintaining or improving good fuel economy and good abrasion resistance.